Simple arithmetic in RATES block?

[peterwadeuk]

Greetings good people :)

I have an application (attempting to use GibbsStudio) in which it seems that I can't define items in a USER_PUNCH.

I am resorting to trying to do the arithmetic in a RATES block, instead. I am not succeeding. Here is my RATES definition:

    kin_HCO3
-start
10 REM
20 kin_ca=1*KIN_DELTA("Portlandite")+2*KIN_DELTA("Larnite")+0*KIN_DELTA("Brucite")+1*KIN_DELTA("Calcite_diss")
30 kin_mg=0*KIN_DELTA("Portlandite")+0*KIN_DELTA("Larnite")+1*KIN_DELTA("Brucite")+0*KIN_DELTA("Calcite_diss")
60 moles = -2*(kin_ca+kin_mg)
70 rem print kin_ca, kin_mg, moles
320 SAVE moles
-end

and here is the accompanying KINETICS block:

KINETICS 1-100
kin_HCO3
    -formula  HCO3-1  1
    -m        0
    -m0       0
    -tol      1e-08

When I "un-rem" line 70, kin_ca, kin_mg, moles are printed in the output file (*.pqo). However, the calculated value for kin_HCO3 is not passed up to the main program.

I would be grateful for direction :)

All the best,
Peter

[dlparkhurst]

The code you have does not look like a typical expression that I would use in RATES. You would have RATES expressions for Portlandite, Larnite, and Brucite that are functions of solution composition and the variable TIME, and each would have -formula in KINETICS that added the appropriate mineral composition.

You should be able to use KIN_DELTA in a USER_PRINT or USER_PUNCH definition to calculate the values that you need. The average rate of a reaction would be KIN_DELTA(...)/KIN_TIME. The total calcium change, in moles, would be as you have defined it.

Code: [Select]

USER_PUNCH
20 kin_ca=1*KIN_DELTA("Portlandite")+2*KIN_DELTA("Larnite")+0*KIN_DELTA("Brucite")+1*KIN_DELTA("Calcite_diss")

KINETICS and RATES are a little tricky because the time that the RATES expression is executed is variable. The expression will be evaluated several times per time step, and the times at which it is evaluated are not necessarily monotonic. So, PRINT statements in the RATES expression are useful for debugging your RATES expression, but a little ambiguous if you transfer them to USER_PUNCH. You can use PUT and GET to transfer values from a RATES expression to USER_PRINT or USER_PUNCH.

[peterwadeuk]

Thank you David